Finger speed issues are almost 100% caused by issues with reading patterns, whether you realize it or not. The longer it takes to read a pattern, the less time you have to move your fingers to actually hit the notes.
I'd suggest trying out some different skins (it can a while to get used to a skin, so don't worry if you feel awkward at first), checking out unranked maps (believe it or not, most of the best maps are unranked), practicing maps converted from other games (namely, stepmania), and focusing on identifying and practicing the specific sort of patterns you have trouble hitting. Watch replays of your plays and look at exactly where you're missing, or losing accuracy, and try to identify which patterns you have the most difficulty with, and actively look for more maps that have those patterns. You've reached a skill level where focused practice becomes more useful.